pngencoder.java

JAVA写成的图表程序,有曲线图

package encoder;

/**
 * PngEncoder takes a Java Image object and creates a byte string which can be saved as a PNG file.
 * The Image is presumed to use the DirectColorModel.
 *
 * Thanks to Jay Denny at KeyPoint Software
 *    http://www.keypoint.com/
 * who let me develop this code on company time.
 *
 * You may contact me with (probably very-much-needed) improvements,
 * comments, and bug fixes at:
 *
 *   [e-mail]
 *
 * This library is free software; you can redistribute it and/or
 * modify it under the terms of the GNU Lesser General Public
 * License as published by the Free Software Foundation; either
 * version 2.1 of the License, or (at your option) any later version.
 *
 * This library is distributed in the hope that it will be useful,
 * but WITHOUT ANY WARRANTY; without even the implied warranty of
 * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the GNU
 * Lesser General Public License for more details.
 *
 * You should have received a copy of the GNU Lesser General Public
 * License along with this library; if not, write to the Free Software
 * Foundation, Inc., 59 Temple Place, Suite 330, Boston, MA  02111-1307  USA
 * A copy of the GNU LGPL may be found at
 * http://www.gnu.org/copyleft/lesser.html,
 *
 * @author J. David Eisenberg
 * @version 1.4, 31 March 2000
 */

import java.awt.*;
import java.awt.image.*;
import java.util.*;
import java.util.zip.*;
import java.io.*;

public class PngEncoder extends Object
{
    /** Constant specifying that alpha channel should be encoded. */
    public static final boolean ENCODE_ALPHA=true;
    /** Constant specifying that alpha channel should not be encoded. */
    public static final boolean NO_ALPHA=false;
    /** Constants for filters */
    public static final int FILTER_NONE = 0;
    public static final int FILTER_SUB = 1;
    public static final int FILTER_UP = 2;
    public static final int FILTER_LAST = 2;

    protected byte[] pngBytes;
    protected byte[] priorRow;
    protected byte[] leftBytes;
    protected Image image;
    protected int width, height;
    protected int bytePos, maxPos;
    protected int hdrPos, dataPos, endPos;
    protected CRC32 crc = new CRC32();
    protected long crcValue;
    protected boolean encodeAlpha;
    protected int filter;
    protected int bytesPerPixel;
    protected int compressionLevel;

    /**
     * Class constructor
     *
     */
    public PngEncoder()
    {
        this( null, false, FILTER_NONE, 0 );
    }

    /**
     * Class constructor specifying Image to encode, with no alpha channel encoding.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @see java.awt.Image
     */
    public PngEncoder( Image image )
    {
        this(image, false, FILTER_NONE, 0);
    }

    /**
     * Class constructor specifying Image to encode, and whether to encode alpha.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @see java.awt.Image
     */
    public PngEncoder( Image image, boolean encodeAlpha )
    {
        this(image, encodeAlpha, FILTER_NONE, 0);
    }

    /**
     * Class constructor specifying Image to encode, whether to encode alpha, and filter to use.
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @param whichFilter 0=none, 1=sub, 2=up
     * @see java.awt.Image
     */
    public PngEncoder( Image image, boolean encodeAlpha, int whichFilter )
    {
        this( image, encodeAlpha, whichFilter, 0 );
    }


    /**
     * Class constructor specifying Image source to encode, whether to encode alpha, filter to use, and compression level.
     *
     * @param image A Java Image object
     * @param encodeAlpha Encode the alpha channel? false=no; true=yes
     * @param whichFilter 0=none, 1=sub, 2=up
     * @param compLevel 0..9
     * @see java.awt.Image
     */
    public PngEncoder( Image image, boolean encodeAlpha, int whichFilter,
       int compLevel)
    {
        this.image = image;
        this.encodeAlpha = encodeAlpha;
        setFilter( whichFilter );
        if (compLevel >=0 && compLevel <=9)
        {
            this.compressionLevel = compLevel;
        }
    }

    /**
     * Set the image to be encoded
     *
     * @param image A Java Image object which uses the DirectColorModel
     * @see java.awt.Image
     * @see java.awt.image.DirectColorModel
     */
    public void setImage( Image image )
    {
        this.image = image;
        pngBytes = null;
    }

    /**
     * Creates an array of bytes that is the PNG equivalent of the current image, specifying whether to encode alpha or not.
     *
     * @param encodeAlpha boolean false=no alpha, true=encode alpha
     * @return an array of bytes, or null if there was a problem
     */
    public byte[] pngEncode( boolean encodeAlpha )
    {
        byte[]  pngIdBytes = { -119, 80, 78, 71, 13, 10, 26, 10 };
        int     i;

        if (image == null)
        {
            return null;
        }
        width = image.getWidth( null );
        height = image.getHeight( null );
        this.image = image;

        /*
         * start with an array that is big enough to hold all the pixels
         * (plus filter bytes), and an extra 200 bytes for header info
         */
        pngBytes = new byte[((width+1) * height * 3) + 200];

        /*
         * keep track of largest byte written to the array
         */
        maxPos = 0;

        bytePos = writeBytes( pngIdBytes, 0 );
        hdrPos = bytePos;
        writeHeader();
        dataPos = bytePos;
        if (writeImageData())
        {
            writeEnd();
            pngBytes = resizeByteArray( pngBytes, maxPos );
        }
        else
        {
            pngBytes = null;
        }
        return pngBytes;
    }

    /**
     * Creates an array of bytes that is the PNG equivalent of the current image.
     * Alpha encoding is determined by its setting in the constructor.
     *
     * @return an array of bytes, or null if there was a problem
     */
    public byte[] pngEncode()
    {
        return pngEncode( encodeAlpha );
    }

    /**
     * Set the alpha encoding on or off.
     *
     * @param encodeAlpha  false=no, true=yes
     */
    public void setEncodeAlpha( boolean encodeAlpha )
    {
        this.encodeAlpha = encodeAlpha;
    }

    /**
     * Retrieve alpha encoding status.
     *
     * @return boolean false=no, true=yes
     */
    public boolean getEncodeAlpha()
    {
        return encodeAlpha;
    }

    /**
     * Set the filter to use
     *
     * @param whichFilter from constant list
     */
    public void setFilter( int whichFilter )
    {
        this.filter = FILTER_NONE;
        if ( whichFilter <= FILTER_LAST )
        {
            this.filter = whichFilter;
        }
    }

    /**
     * Retrieve filtering scheme
     *
     * @return int (see constant list)
     */
    public int getFilter()
    {
        return filter;
    }

    /**
     * Set the compression level to use
     *
     * @param level 0 through 9
     */
    public void setCompressionLevel( int level )
    {
        if ( level >= 0 && level <= 9)
        {
            this.compressionLevel = level;
        }
    }

    /**
     * Retrieve compression level
     *
     * @return int in range 0-9
     */
    public int getCompressionLevel()
    {
        return compressionLevel;
    }

    /**
     * Increase or decrease the length of a byte array.
     *
     * @param array The original array.
     * @param newLength The length you wish the new array to have.
     * @return Array of newly desired length. If shorter than the
     *         original, the trailing elements are truncated.
     */
    protected byte[] resizeByteArray( byte[] array, int newLength )
    {
        byte[]  newArray = new byte[newLength];
        int     oldLength = array.length;

        System.arraycopy( array, 0, newArray, 0,
            Math.min( oldLength, newLength ) );
        return newArray;
    }

    /**
     * Write an array of bytes into the pngBytes array.
     * Note: This routine has the side effect of updating
     * maxPos, the largest element written in the array.
     * The array is resized by 1000 bytes or the length
     * of the data to be written, whichever is larger.
     *
     * @param data The data to be written into pngBytes.
     * @param offset The starting point to write to.
     * @return The next place to be written to in the pngBytes array.
     */
    protected int writeBytes( byte[] data, int offset )
    {
        maxPos = Math.max( maxPos, offset + data.length );
        if (data.length + offset > pngBytes.length)
        {
            pngBytes = resizeByteArray( pngBytes, pngBytes.length +
                Math.max( 1000, data.length ) );
        }
        System.arraycopy( data, 0, pngBytes, offset, data.length );
        return offset + data.length;
    }